Fins N Things is a 9-mile loop in the Sand Flats Recreation Area that rolls up and over sandstone fins, one after another. It's less famous than Hell's Revenge but just as fun, and it's quieter. Most tours that include it run 3.5 to 5 hours and cover both trails.
Most Moab trails, including Hell's Revenge and Fins N Things, are in the Sand Flats Recreation Area, which charges a small day-use fee per vehicle. Many tours include it. If you rent, check whether your rental does.